Field of the Invention
The present invention relates to a hydraulic damping mount, more particularly for use as a support for mounting a spring strut, comprising an outer sleeve, an inner sleeve for securing thereto at least one component activatable in at least one direction, an elastomeric body and two chambers charged with a hydraulic damping fluid and in fluidic communication. The inner sleeve comprises a radially projecting boss that separates the two chambers from one another.
A hydraulic damping rubber mount is known from European patent EP 0 456 959 B1. There, between the boss protruding from the inner sleeve and the outer sleeve is an insert for configuring a fluid communication between the two chambers. Manufacturing that mount is thus relatively complicated.
When activated, the inner sleeve is displaced relative to the outer sleeve, preferably axially, so that there is a change in volume of the two chambers. Equalizing the volume is done by the flow of hydraulic fluid via the communication between the two chambers, whereby the resulting hydraulic damping effect counteracts the activation. In this known mount this hydraulic damping effect is effective also when activated externally even at low frequencies. This is why the mount features high stiffness in the higher frequency range. Thus, even an activation of small amplitude is communicated to the outer sleeve and the result is a noise nuisance.
Communicating such small amplitudes is undesirable, especially to the outer sleeve in automotive engineering applications and thus the stiffness of the mount needs to be low, if possible below the static stiffness level when activated at critical frequencies. However, as soon as a high amplitude activation occurs with a low frequency, for instance when the vehicle negotiates a curb, the stiffness of the mount needs to be high. It is only by means of this high stiffness that a high amplitude activation can be accommodated without damage to the mount.
It is accordingly an object of the invention to provide a hydraulic damping mount, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for a mount with enhanced stiffness response with uncomplicated manufacture.
With the foregoing and other objects in view there is provided, in accordance with the invention, a supporting mount for a spring strut having a piston rod and a spring, comprising:
a hydraulic damping mount formed with an inner sleeve to be seated on the piston rod, the inner sleeve having a radially projecting boss, and an outer sleeve having a radially projecting plate for supporting the spring;
an elastomeric body connecting the inner sleeve to the outer sleeve and forming therewith two fluidically connected chambers charged with a hydraulic damping fluid;
the boss of the inner sleeve and the outer sleeve defining an annular gap therebetween connecting the chambers;
the elastomeric body having a substantially cylindrical shape and projecting from an underside of the plate of the outer sleeve and having a frontal bearing surface for supporting the spring of the spring strut; and
an envelope of elastomeric material having a variable thickness surrounding the boss.
In other words, the objects are achieved by a mount of the aforementioned kind in that the fluid communication is configured as a gap between the boss and the outer sleeve so that when activated the fluid flow through the gap is in the direction opposite to the movement of the boss. Furthermore, the xe2x80x9cinnerxe2x80x9d elastomeric body (between the sleeves) and the xe2x80x9couterxe2x80x9d elastomeric body (on which the spring is supported) are formed substantially in one piece.
The insert provided in the prior art mount can now be totally eliminated, resulting in fewer component parts being necessary to thus substantially simplify assembly.
Furthermore, the stiffness response as compared to the prior art mount is now substantially enhanced. Since the boss is attached to the inner sleeve for connection to an activated component the hydraulic fluid now flows in the opposite direction of the movement of the boss when activated, whilst avoiding the fluid being entrained in the movement of the boss. Due to the fluid flow contrary to the direction of activation the stiffness can now be reduced down to attaining the natural frequency of the fluid flow. In this arrangement the boss may be configured ring or star-shaped or fingered in form.
This results in the stiffness of the mount when activated by a small amplitude now no longer increasing, or only negligably up to a critical frequency. Indeed, depending on the hydraulically effective surface area to the cross-section of the fluid communication the dynamic stiffness can be reduced to below the static stiffness, also termed xe2x80x9cunderswing.xe2x80x9d In this arrangement, the hydraulically effective surface area substantially corresponds to the surface area of the boss at the inner sleeve. When using a round boss and a round outer sleeve the cross-section in the fluid communication connection is circular. As long as the ratio between the hydraulically effective surface area and the cross-section is less than unity the desired reduction in stiffness is achievable.
The critical frequency at which the mount gains in hardness, causing a corresponding increase in the stiffness, depends on the cross-section of the fluid communication connection and on the mass of the fluid in this connection. This frequency increases, the larger the cross-section, and decreases, the higher the mass flow, for example due to an elongation of the fluid communication connection, it being a natural frequency of the fluid oscillating in the connection. This is why it can be altered in the mount in accordance with the invention by varying the diameter and/or thickness of the boss, i.e. tailoring it to the individual circumstances. There is no need to alter the outer sleeve.
It is advantageous for the boss to be enveloped in an elastomeric material. By varying the thickness of this envelope the cross-section and length of the fluid communication connection can be altered in thus setting the response of the mount. Furthermore, this envelope prevents the outer sleeve from being damaged due to prohibitively high activation, i.e. it serving as an inner stop.
In accordance with an added feature of the invention, the inner sleeve is elongated into an elongated portion of the outer sleeve. The elastomeric body then extends into the interspace between this portion and the inner sleeve in achieving the static stiffness of the mount in accordance with the invention.
In this arrangement the outer sleeve may be configured split in such a way to advantage that the first part forms the section of the larger diameter outer sleeve and the radially inswept flange, whilst the second part of the outer sleeve provides the elongated portion.
When the mount is configured to support a spring strut with a piston rod a bearing surface is provided for supporting a spring. The piston rod is supported by the hydraulic damping mount as described above and secured to the inner sleeve.
Advantageously, the supporting mount comprises an upper and a lower plate having projecting, substantially cylindrical portions forming the outer sleeve. Making use of separate plates substantially facilitates manufacture and assembly of the supporting mount.
In accordance with one advantageous further embodiment the projecting portion of the lower plate translates into a substantially conical portion. This conical portion provides a buffer for stopping the spring strut in preventing prohibitively large loads and displacements. Optionally it may serve to mount a helper spring.
In another advantageous aspect the lower plate comprises a further portion projecting in the direction of the upper plate and protruding into the portion of the upper plate, it being this further portion that centre-locates the two plates.
Further advantage is obtained in that the elastomeric body extends sandwiched between the two plates, it possibly covering the full surface area of one of the two plates in achieving a reliable seal of the chambers and the fluid communication connection. It is this arrangement that prevents any relative displacements of the plates in operation causing a noise nuisance.
In another advantageous further embodiment the bearing surface supporting the spring is supported independently of the inner sleeve, such a version of the supporting mount being termed decoupled in permitting achieving optimum noise vibration insulation and ride.
The supporting mount preferably has several bolts for securing it to the vehicle body. These bolts pass through both plates to thus simultaneously locate and fix them in place on the body.
The fact that the elastomeric body is configured integrally in one piece simplifies design and manufacture.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a hydraulic damping mount, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.